Better ICMP code encapsulation

1 files changed, 96 insertions, 23 deletions

diff --git a/icmp.c b/icmp.c
index 63436ac..bef1fd6 100644
--- a/icmp.c
+++ b/icmp.c
@@ -1,24 +1,28 @@
 #include <stdlib.h>
+#include <stdbool.h>
 #include <stddef.h>
 #include <string.h>
 #include <assert.h>
 #include <unistd.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
+#include <netinet/ip.h>
 #include <netinet/ip_icmp.h>
 #include <arpa/inet.h>
-#include "icmp.h"
+#include "icmp_client.h"
+#include "icmp_server.h"
 #include "util.h"
 
 
-#define PROT_ICMP 1
-
-
-static void make_sockaddr(struct sockaddr_in *dst, const char *ip_address) {
+static void make_sockaddr_u32(struct sockaddr_in *dst, uint32_t addr) {
 	memset(dst, 0, sizeof *dst);
 	dst->sin_family = AF_INET;
 	dst->sin_port = htons(0);
-	dst->sin_addr.s_addr = inet_addr(ip_address);
+	dst->sin_addr.s_addr = addr;
+}
+
+static void make_sockaddr(struct sockaddr_in *dst, const char *ip_address) {
+	make_sockaddr_u32(dst, inet_addr(ip_address));
 }
 
 static uint16_t compute_checksum(const void *buf_, size_t buflen) {
@@ -39,18 +43,27 @@ static uint16_t compute_checksum(const void *buf_, size_t buflen) {
 	return res;
 }
 
-int icmp_open_socket(void) {
-	return socket(PF_INET, SOCK_DGRAM, PROT_ICMP);
+int icmp_client_open_socket(void) {
+	return socket(PF_INET, SOCK_DGRAM, IPPROTO_ICMP);
 }
 
-struct icmp_reply icmp_communicate(int sock, const char *ip_address, int seqnum, const void *data_, size_t length) {
+int icmp_server_open_socket(void) {
+	return socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
+}
+
+struct icmp_client_incoming icmp_client_communicate(
+		int sock, const char *ip_address,
+		int id, int seqnum,
+		const void *data_, size_t length) {
+
 	static uint8_t buffer[ICMP_MAX_PAYLOAD_LENGTH];
 
 	const uint8_t *data = (const uint8_t*)data_;
 
 	assert(length <= ICMP_MAX_PAYLOAD_LENGTH);
 
-	struct icmp_reply errret = (struct icmp_reply){.data = NULL, .length = 0, .seqnum = 0};
+	struct icmp_client_incoming errret =
+			(struct icmp_client_incoming){.data = NULL, .length = 0, .id = 0, .seqnum = 0};
 
 	struct sockaddr_in addr;
 	make_sockaddr(&addr, ip_address);
@@ -59,7 +72,8 @@ struct icmp_reply icmp_communicate(int sock, const char *ip_address, int seqnum,
 	memset(&msg, 0, sizeof msg);
 	msg.type = ICMP_ECHO;
 	msg.code = 0;
-	msg.seqnum = seqnum;
+	msg.id = htons(id);
+	msg.seqnum = htons(seqnum);
 
 	memcpy(msg.payload, data, length);
 
@@ -90,25 +104,90 @@ struct icmp_reply icmp_communicate(int sock, const char *ip_address, int seqnum,
 
 	memcpy(buffer, msg.payload, payloadlen);
 
-	return (struct icmp_reply){
+	return (struct icmp_client_incoming){
 		.data = buffer,
 		.length = payloadlen,
-		.seqnum = msg.seqnum
+		.id = ntohs(msg.id),
+		.seqnum = ntohs(msg.seqnum)
 	};
 }
 
-int icmp_send_echo_reply(const char *ip_address, int id, int seqnum, const void *data_, size_t length) {
+struct icmp_server_incoming icmp_server_receive(int sock) {
+	static uint8_t buffer[ICMP_MAX_PAYLOAD_LENGTH];
+
+	struct icmp_server_incoming errret =
+			(struct icmp_server_incoming){.data = NULL, .length = 0, .id = 0, .seqnum = 0, .source_addr = 0};
+
+	char buf[MAX_IP_PACKET_SIZE];
+
+	struct iovec iov1;
+	memset(&iov1, 0, sizeof iov1);
+	iov1.iov_base = buf;
+	iov1.iov_len = sizeof buf;
+
+	struct msghdr recv_msghdr;
+	memset(&recv_msghdr, 0, sizeof recv_msghdr);
+	recv_msghdr.msg_name = NULL;
+	recv_msghdr.msg_iov = &iov1;
+	recv_msghdr.msg_iovlen = 1;
+
+	// TODO: check whether the above stuff needs re-initialisation
+	while (true) {
+		recv_msghdr.msg_flags = 0;
+
+		ssize_t nr = recvmsg(sock, &recv_msghdr, 0);
+		if (nr < 0) return errret;
+
+		// buf now contains received data starting at the IP header
+
+		// printf("Full packet received:\n");
+		// xxd(buf, nr);
+
+		struct iphdr *hdr = (struct iphdr*)buf;
+		int hdr_len = hdr->ihl * 4;
+		uint32_t saddr = hdr->saddr;
+
+		struct icmp_echo *msg = (struct icmp_echo*)(buf + hdr_len);
+		int msg_len = nr - hdr_len;
+		int payloadlen = msg_len - offsetof(struct icmp_echo, payload);
+		// printf("Received: type %u   code %u   id %hu   seqnum %hu   payload:\n",
+		//         (unsigned)msg->type, (unsigned)msg->code, msg->id, msg->seqnum);
+		// xxd(msg->payload, payloadlen);
+
+		if (msg->type != ICMP_ECHO && msg->type != ICMP_ECHOREPLY) {
+			// printf("Not an ICMP_ECHO or ICMP_ECHOREPLY, ignoring\n");
+			continue;
+		} else {
+			memcpy(buffer, msg->payload, payloadlen);
+
+			return (struct icmp_server_incoming){
+				.data = buffer,
+				.length = payloadlen,
+				.type = msg->type,
+				.id = ntohs(msg->id),
+				.seqnum = ntohs(msg->seqnum),
+				.source_addr = saddr
+			};
+		}
+	}
+}
+
+int icmp_server_send_reply(
+			int sock, uint32_t addr_u32,
+			int id, int seqnum,
+			const void *data_, size_t length) {
+
 	const uint8_t *data = (const uint8_t*)data_;
 
 	struct sockaddr_in addr;
-	make_sockaddr(&addr, ip_address);
+	make_sockaddr_u32(&addr, addr_u32);
 
 	struct icmp_echo msg;
 	memset(&msg, 0, sizeof msg);
 	msg.type = ICMP_ECHOREPLY;
 	msg.code = 0;
-	msg.id = id;
-	msg.seqnum = seqnum;
+	msg.id = htons(id);
+	msg.seqnum = htons(seqnum);
 	msg.checksum = 0;
 
 	memcpy(msg.payload, data, length);
@@ -117,13 +196,7 @@ int icmp_send_echo_reply(const char *ip_address, int id, int seqnum, const void
 
 	msg.checksum = ~compute_checksum(&msg, total_length);
 
-	int sock = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
-	// The below is only necessary for sending on IPPROTO_RAW sockets
-	// int zero = 0;
-	// assert(setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &zero, sizeof zero) >= 0);
-
 	int ret = sendto(sock, &msg, ICMP_PAYLOAD_OFFSET + length, 0, (struct sockaddr*)&addr, sizeof addr);
-	close(sock);
 	if (ret < 0) return -1;
 
 	return 0;